Page 187 - Practical Ship Design

Volume. Arm mid Dimension-Based Designs I53

Number of underdeck containers (20 x 8 x 8)

Fig. 5.4. Number of containers carried under deck versus numbers in the midship section and ship
speed.

rather surprising possibility that there are a number of ranges of container numbers
for which optimum ships can be designed with intervening numbers which require
an acceptance of some dimensional proportions that take the ship away from the
optimum.
Speed has an effect on the container numbers that can be carried in a ship of
certain dimensions partly because of its influence on the block coefficient and
partly because of its influence on machinery power and thus on the engine room
dimensions.
Figure 5.4 reproduced from the 1976 paper shows the under-deck container
numbers which give economic container ships for various speeds. It also shows the
tier x row numbers for which the midship section would be arranged. The value of
this figure could have been improved, particularly in these days of wholly open
container ships, if the abscissa had been total containers rather than under deck
containers.

5.7.2 Open container ships
Container ships without hatch covers represent possibly the latest major ship
design development and are a nice example of the fact that major improvements
stem from lateral thinking rather than from optimisation techniques. One thing this
type of ship confirms is the contention that container ships are controlled by
stability rather than by volume or weight.
One great advantage of these “open” container ships is the fact that all the
containers carried are in cells and no lashing is needed. A second advantage is the